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    <script>
      // 题目1(选做)：const arr=['name','age','hhh','hhh','age','hhh','hhh','hhh'] 元素各出现多少次
      // 要求输出一个对象如下：{age: 2,hhh: 5,name: 1}
      const arr = ['name', 'age', 'hhh', 'hhh', 'age', 'hhh', 'hhh', 'hhh']
      let obj = {}
      for (let i = 0; i < arr.length; i++) {
        if (obj[arr[i]]) {
          obj[arr[i]]++
        } else {
          obj[arr[i]] = 1
        }
      }
      console.log(obj)

      // 题目2(必做)：现在两个数组，判断在a中的元素，不在b中 const a = [1,2,3,5] const b=[1,3,5,6] 将在a不在b中的筛选出来
      // 要求：输出一个数组：[2]
      const a = [1, 2, 3, 5]
      const b = [1, 3, 5, 6]
      let c = []
      for (let i = 0; i < a.length; i++) {
        if (b.indexOf(a[i]) === -1) {
          c.push(a[i])
        }
      }
      console.log(c)

      // 题目3(必做):数组去重(可以用多种方法,至少写一种)
      // 要求：输出一个数组：[1,2,3,9]
      // filter indexof 方法
      const arr2 = [1, 2, 3, 2, 9]
      let res = arr2.filter((item, index, array) => {
        return array.indexOf(item) === index
      })
      console.log(res)
      // set 方法
      const res2 = new Set(arr2)
      console.log(res2)
    </script>
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